AudioVideo: add avTranscoder lib dependency
AudioVideo: update Reader plugin

* Use AvTranscoder instead of libAv.
* One exception: still use libAv in PluginFactory.
* Th plugins manages only one video stream.
* PluginProcess:
	* read next frame of source image.
	* set image to encode, depending on value of OFX params.
	* use colorTransform to convert source image to image to encode.
gitignore: ignore TuttleOFX-Data-MXF